The SATRACK System: Development and Applications


INTRODUCTION
SATRACK was developed to validate and monitor
the Trident missile guidance error model in the System
Flight Test Program. It is the primary instrumentation
and processing system responsible for accuracy evaluation
of the Navy’s Strategic Weapon System. Instrumentation
and processing systems available when the
Trident Development Program began could not meet
this need. APL conceived and led the development of
the SATRACK system to fulfill this requirement. Prototype
instrumentation required for the missile and
ground station data collection functions were developed
at APL to validate the concept, and we generated
specifications controlling the development of the operating
missile and ground station hardware.


BASIC CONCEPTS

The SATRACK concept is shown in Fig. 1. Signals
from GPS satellites are relayed by the test missile to
receiving equipment at a launch-area support ship
(LASS) and a downrange support site (DRSS). At the
beginning of the Trident Flight Test Program a ship was
used for downrange support; now that support is provided
by a land station. The missile hardware was
called a translator to emphasize that no signal tracking
functions are accomplished in the missile (i.e., the
signals are simply “translated” to S-band and retransmitted).


SATRACK EVOLUTION
SATRACK I

The C4 missile design was well under way before it
was decided to implement the SATRACK system. The
proposed design approach did minimize the required
additional missile electronics and it did take advantage
of the existing S-band antenna; however, a new GPS
antenna had to be added. The C4 design constraints
held the GPS antenna configuration to four elements
spaced uniformly around the missile circumference.


SATRACK II
The development of the Trident II (D5) missile
began in 1981. To support this development, APL
conducted the Accuracy Evaluation System study.
That study supported development of the technical
objectives and guidelines document that defined the
accuracy evaluation requirements for the D5 Missile
Flight Test Program. The SATRACK II requirements,
defined by the Accuracy Evaluation System study,
included significant performance enhancements.